1. Field of the Invention
This invention relates to a method for the production of a semiconductor device and more particularly to an improved process for the formation of an interlevel insulator which flattens surface irregularities over the semiconductor substrate of the device.
2. Description of the Prior Art
In order to improve the degrees of density and integration of semiconductor devices, it is essential to form its wiring in three dimensions. The wiring in three dimensions may give rise to surface irregularities over the semiconductor substrate of the device, which irregularities will cause disconnection and/or electrical short circuiting of the wiring, thereby decreasing the production yield of the device. For the purpose of solving these problems,, it is desirable to flatten the surface of an insulating film which is formed on a conductive film used for lower wiring. The conventional method commonly used for this purpose at the present time includes the steps of: applying organic silanol glass, so that the concave portions of the insulating film which is formed on the conductive film are filled therewith; and hardening the organic silanol glass by the application of heat to form an insulating film made of organic silanol glass, so that the surface irregularities of the insulating film formed on the conductive film are flattened.
In the above-mentioned conventional method, because single application of organic silanol glass cannot provide satisfactory flatness, the flat surface of the insulating film formed on the conductive film has been attained by several applications of organic silanol glass. However, a thick insulating film made of organic silanol glass gives rise to a crack 9 as shown in FIG. 2, thereby causing insulation failure.
If the number of applications of organic silanol glass is decreased, satisfactory flatness cannot be obtained, so that there will occur disconnection 10 of the upper conductive film 8 as shown in FIG. 3.
Moreover, when after the insulating film 4 made of organic silanol glass is formed and the surface irregularities are flattened, the interlevel insulator, which comprises the insulating film 4 made of organic silanol glass and other insulating films 3 and 5, is provided with a through-hole 11, etc., followed by formation of the upper conductive film 8 to connect electrically with the lower conductive film 2, some gases such as O.sub.2 and H.sub.2 O are generated in the insulating film 4 made of organic silanol glass and diffuse into the upper conductive film 8 through a certain portion of the insulating film made of organic silanol glass, which portion is exposed to the side wall of the through-hole 11. These gases react with metal materials used for wiring to form metal oxides. As a result, the connection resistance between the lower conductive film 2 and the upper conductive film 8 increases, so that their electrical connection becomes unstable, thereby causing difficulties in producing high-speed semiconductor devices.